The aim of this paper is to shed some light on the issue of how we can understand constitutive rules as being in force for participants S in some rule-constituted practice. We take a look on complicated team-games that are broadly conceived as model example of rule-constituted practices. We claim that rules of games are dependent on mental states of participants in that practice. More precisely, they are in force for the participants S of such games if these participants jointly meet the following conditions: (1) every S has a…